This invention relates generally to motion transducers, and more particularly to transducers for motion having an angular relation to the direction of the axis of an Eddy current displacement sensor.
There are many known requirements for sensing motion having considerable travel distances. Many distances of interest fall in the range of from a few tenths of an inch to several inches or even tens or hundreds of inches. Various technologies have been applied to this problem measurement area. Optical grids on either a fixed or moving element have been used with small sections of a similar optical grid with a light sensor on the opposing element. One linear motion sensor is a linear variable differential transformer (LVDT) type of a device. In such an LVDT, a primary winding and two secondary windings are provided on one element. An armature or iron core is provided on a second element, inside the structure holding the windings. The magnetic coupling between the primary and secondary coils depends on the linear position of this armature in relation to the two secondary windings. Such LVDT devices have relatively low cost, solid robust characteristics for a wide variety of environments, and very good resolution.
Various eddy-current displacement sensors have been used for detecting small motions between a fixed coil and a conducting surface. As the distance between the fixed coil and the conductive surface changes, eddy currents are induced in the material of the conducting surface. The effect of these eddy currents is reflected into the fixed coil, and this in effect changes the apparent resistance and inductance of the fixed coil. Such eddy current displacement sensors are generally used only for detecting small changes in the distance between the fixed coil and the conducting surface. Such devices are typically useful only for measurements of distance of a few millimeters for the gap between the fixed coil and the conducting surface. If such an eddy-current displacement sensor is used to measure the distance between a fixed coil and a conductive surface, and the conducting surface is inclined with respect to the magnetic axis of the fixed coil, the change in gap as the conductive surface is moved in relation to the magnetic axis, the eddy-current effect in the fixed coil may then be interpreted as a measure of that movement normal to the magnetic axis.